Averaging of temporal memories by rats.

Rats were trained on a mixed fixed-interval schedule in which stimulus A (tone or light) indicated food
availability after 10 s and stimulus B (the other stimulus) indicated food availability after 20 s. Testing
consisted of nonreinforced probe trials in which the stimulus was A, B, or the compound AB. On
single-stimulus trials, rats responded with a peak of activity around the programmed reinforced time. On
compound-stimulus trials, rats showed a single scalar peak of responding at a time midway between those
for stimulus A and B. These results suggest that when provided with discrepant information regarding the
temporal predictability of reinforcement, rats compute an average of the scheduled reinforcement times for the
A and B stimuli and use this average to generate an expectation of reward for the compound stimuli.